The present invention relates to the regulation of the thrust of a propulsion system and concerns more particularly a device for varying the thrust of a propulsion system using a solid propellant.
The variation in the modulus of the thrust vector of a propulsion system may be obtained either by varying the flow of the gases or by deviating a part of the gases axially in a direction opposed to the main thrust or radially in a symmetrical manner.
The variation in the flow may be effected either directly by controlling the quantity of propellant at the inlet of the chamber or indirectly by regulating the outlet section of the chamber.
In the case of a liquid propellant, the control of the flow at the inlet of the chamber presents no difficulty. 0n the other hand, in the case of a solid propellant, in respect of which the combustion chamber performs at the same time a storage function, only the solution of the regulation of the outlet section can be used in the region of the throat of the nozzle.
When a propellant whose combustion rate is very sensitive to pressure is used, any variation in the section of the throat of the nozzle produces a variation in the combustion pressure and consequently a variation in the flow.
Various devices for regulating the section of a nozzle are already known. Among the prior art there may be cited in particular U.S. Pat. Nos. 3,069,846 and 3,192,710 which disclose devices comprising needle-valves disposed upstream of the throat of the nozzle.
U.S. Pat. No. 3,069,846 relates to a thrust regulating device comprising a closure member formed by a rising valve member whose conical head extends into the throat of the nozzle and which is actuated by an electromagnet.
This device entails a bent path for the outlet of the gases. It is consequently bulky and inapplicable in many cases.
U.S. Pat. No. 3,192,710 discloses a device in which an annular cam mounted around the nozzle is actuated by motors for shifting the nozzle itself axially with respect to a fixed probe or needle.
This device is also bulky owing to the necessary position of its components around the convergent-divergent structure and this bulkiness also limits its applications. U.S. Pat. Nos. 3,726,480 and 3,943,708 disclose devices in which a movable element, or needle, is disposed in the nozzle on the downstream side with respect to the flow of the gases and is displaced axially in the throat of the nozzle by a system of jacks.
Not only is the mechanism of these devices relatively complicated, it is completely immersed in the hot gases which at least impairs the operation of the device whose thermal insulation is extremely difficult to achieve.